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The Sony warehouse was destroyed by fire and the client wished to rebuild the warehouse on the same footprint. The site is located on a secondary aquifer (Kempton Park Gravel) overlaying London Clay. Groundwater was encountered between 1.78m and 1.88m bgl within the Kempton Park Gravels. A site investigation revealed a contaminated groundwater plume beneath the warehouse with elevated concentrations of hydrocarbons. Although the levels were not a risk to human health risk, they were deemed to pose an environmental risk. The concentrations of PAH, TPH and BTEX were >100ug/l, >10,000ug/l) and >2000ug/l respectively.
With the programme already underway for reconstructing the warehouse, Cognition was approached by ISG for advice on possible measures for remediating groundwater beneath the warehouse. The two most suitable options for dealing with this type on contamination with the underlying geology are Soil Vapour Extraction (SVE)/Multiphase Extraction (MPE) and in situ oxidation. Given the tight programme for redeveloping the site, in situ oxidation was selected as the quickest, most effective and least disruptive remediation option.
Cognition designed a solution based on installing perforated dosing pipework beneath the new concrete slab with dosing points located outside the warehouse in case additional dosing was needed. Cognition installed six lengths of 100mm diameter perforated pipe each 90m in length and 1m deep beneath the slab; the location of the pipework has been determined partly by the layout of concrete pads and foundation structures but consideration has also been given to optimising the coverage across the footprint. The pipes also made use of hydraulic gradient to allow oxidants to spread through the groundwater covering the entire area of the development.
The main elements were as follows:
Cognition successfully installed the dosing system and carried out dosing of oxidising chemicals. As well as acting directly on the contaminants, the chemicals increased oxygen concentrations in groundwater encouraging natural attenuation from indigenous bacteria present in the soil and groundwater. The client’s consultant continued to monitor the impact of the contamination plume and results indicated that the dosing had reduced concentrations to acceptable levels. Should further deterioration become evident additional doses can be added to the system. The solution proved to be a rapid cost effective means of dealing with the contamination whilst minimising disruption to the warehouse reconstruction.